The use of showers in personal hygiene is widespread in the United States and a pleasure to most users. In a shower, the water is normally continuously running and the result is excess consumption. Thus, showers provide a major opportunity in water conservation. Fixed-rate low-flow showerheads are well known. However, some users find these low-flow showerheads undesirable for many purposes, such as washing the hair, because of inadequate flow. Standard shower flow heads can be used and, to achieve conservation, the user can rely upon manual adjustment of the main hot and cold shower water rate valves. This requires a great deal of adjustment and dexterity beyond the ability or concern of most people for water conservation. Some showerheads have a simple on/off valve. However, such showerheads suffer the disadvantage and danger of sudden temperature changes since, when in the off condition, the hydrodynamics of the hot and cold water supplies and their pressure differentials usually result in a water temperature change when next turned on. Since hot and cold line pressures and temperatures change from time to time, such valves cannot be relied upon to provide the same water temperature mix as was present when the showerhead was turned off. When such a showerhead is next turned on, the mixed water may be either scalding hot or freezing cold until the manual valves are adjusted to the desired output temperature. Thus, there remains a need for a shower water supply and control system which minimizes shower water flow, which minimizes temperature changes, and which yet provides an opportunity for a larger rinse flow together with significant water conservation.